The invention relates generally to data communications systems and in particular to a method and apparatus for operating a token passing ring network.
Token passing ring networks are commonly used for computer or data processing communications. They typically operate at very high data rates; and to use the network, a station or node must possess the "token" which enables the node to transmit data.
Perhaps the most serious deficiency of the token passing ring network is network latency; that is, if many or all nodes of the network require access to the network, then each user must wait a much longer time than if the network were idle. This corresponds to the relatively slow "passing" of the token from user to user. Several methods have been employed for reducing the latency time. For example, an increase of bandwidth on the network bus (and the cost attendant therewith) allows a higher data rate to be employed along the bus thereby reducing the "transit time" around the bus. As noted above, however, increasing the bandwidth of the bus is an expensive approach to solving the latency problem and may require the bus to have substantial excess capacity during the normal, non-peak, use times.
Other systems have employed a time division multiplex whereby one or more nodes is allotted a specific time slot according to the repeating repetition rate of the system. This reduces the rate of transmission for each individual transmitting node and if all nodes are transmitting onto the line, does little to reduce the network latency.
It is therefore an object of the invention to reduce network latency in token passing ring networks while maintaining reasonable manufacturing costs and high reliability. Another object of the invention is reducing network latency in existing ring networks.